these are valid points but the conversion of mass to energy doesn't address how mass interacts with mass. And yes cars would attract other cars to each other, even if only on an infintesimal scale. Drop something off the edge of a flat plane, falling along another flat plane and watch what happens. As for gravity it is the attempt of conservation of energy to place all potential expressions of energy at the lowest baseline. In the face of an overwhelming magnetic attraction to a central point someone can confuse the appearance of a curvature of space. Is it the sphere? Makes sense, but the sphere is the most condense way to store mass in one place as tightly packed as possible, the natural byproduct of electron fields. Try again friend.